The present invention relates to a video signal record/playback device for use in a video tape-recoder, for example. More particularly, the invention relates to an improvement of a comb filter, which is used in the video tape-recorder.
For recording a video signal in the video tape-recorder, the video signal is generally separated into a luminance signal and a color signal. The luminance signal is frequency modulated, while the color signal is frequency-converted into a low frequency. Then, both signals are mixed and recorded into a magnetic tape.
For playing back the video signal, the crosstalk removal or the drop-out compensation are performed by using a 1H-corelation of the video signal (H is a horizontal scanning period).
A 1H delay line is used for each of video signal separation, crosstalk removal, and drop-out compensation.
However, if the 1H delay lines are used for those processings, the cost of manufacturing is increased, and material use is inefficient.
Japanese Patent Disclosure (KOKAI) No. 55-82583, published on June 21, 1980 (inventor: J. Hirai) discloses a video signal record/playback device in which the three processings as mentioned above can be realized by a single 1H delay line.
In the video signal record/playback device disclosed by the patent disclosure, the output signal from the video signal record/playback device is produced in the form of a video signal in a playback mode.
In use of this device, a noise canceller generally provided in the video tape-recorder is set at the prestage of the comb filter. This is because the signal which can be treated by the noise canceller is the luminance signal, not the video signal.
Provision of the noise canceller at the prestage of the comb filter, however, distorts the waveform of the video signal and deteriorates the quality of the resultant picture.
That is, the noise canceller, to be described later, takes a noise component out of the luminance signal, and subtracts the noise component from the luminance signal, thereby obtaining a luminance signal containing no noise component. In this case, since the peak-to-peak value of the noise component is large at the prestage of the comb filter, the level of the high component of the luminance signal, which is contained in the noise component for subtraction, is large. As a result, the high component is removed by the subtraction operation, and a waveform of the luminance signal is distorted.
Further, in the video signal record/playback device disclosed in the patent disclosure, the comb filter has many adders and subtractors. The characteristics of the comb filter depend largely on the variation of adding and subtracting ratios of the adders and subtractors. In this respect, the adding and subtracting ratios must by exactly fixed. In the case where the number of the adders and subtractors is great, to fix the ratios at desired values is troublesome and time-consuming, and if they are not correctly fixed, the characteristics of the filter are further degraded, and the picture quality is deteriorated.